1. Field of the Invention
The present invention relates to a multilayer printed wiring board manufacturing apparatus and method and a laser processing apparatus, particularly to a multilayer printed wiring board manufacturing apparatus and method to form fine holes at a low cost and a laser processing apparatus.
2. Description of Related Art
A build-up multilayer wiring board alternately has interlayer resin insulators and conductive circuit layers, provides holes to the interlayer resin insulator layers and then electrically connects the upper layers and lower layers by forming conductive films at the wall surface of these holes.
A hole (via hole) of the interlayer resin insulating layer is generally formed through the exposure and developing process by giving photosensitive property to the interlayer resin.
However, the diameter of these via holes on the multilayer printed wiring board is almost 100 μm or less and it is expected to develop the technology to form the via hole having still smaller diameter. Because of such requirement, employment of the processing method utilizing the laser beam for the boring of the build-up multilayer wiring board is now investigated.
A technology using laser for the boring is proposed, for example, in the Japanese Published Examined Patent No. HEI 3-54884. In this technology, a light beam from the laser source is received by a processing head for deflection. Thereby the laser beam is irradiated to a predetermined resin insulator to form a through hole.
However, a multilayer wiring board has via holes in one layer in the number ranging from several hundreds to several tens of hundred and is also required to have higher positional accuracy because the via holes must be electrically connected with conductive circuits of the lower layer. Therefore, it has been required to enable the positioning of laser with higher accuracy in order to realize mass-production of the multilayer printed wiring board.
Namely, it is required to accurately measure the substrate position to embody the automatic control for mass production.
As a method of measuring the substrate position, an ordinary method has been introduced in which a positioning mark provided on the substrate is read with a camera to measure the position.
However, in the case of a multilayer printed wiring board, the positioning marks are often formed on a lower layer of the resin layer to be eliminated by a laser beam and if it is attempted to read the light beam reflected from the positioning mark under the resin layer, it is sometimes difficult to accurately read the reflected beam through reflection by the resin layer.
Therefore, the inventors of the present invention has proposed, as a method of accurately reading the positioning mark, to read the positioning mark from a silhouette by making use of the transmitting light beam of the light applied to the multilayer printed wiring board from the lower side.
However, since the multilayer printed wiring board is placed on an X-Y table, when the light is applied to the substrate from the lower side, it is thought that the table itself or a driver motor for driving the table will interfere the application of light beam.
Moreover, since the substrate is always moving by means of the X-Y table, it is also difficult to always apply the light beam from the lower side of the positioning mark which moves in combination with the X-Y table. Moreover, a problem like this arises not only in the multilayer printed wiring board but also in automatic laser process.
On the other hand, in order to bore the via holes and through holes of the multilayer printed wiring board, a laser beam in such a wavelength as generating heat in the interlayer resin must be used and the CO2 laser or excimer laser are considered as such laser source. The excimer laser has the wavelength as short as 248 nm in KrF, 308 nm in XeCL and 193 nm in ArF are and is suitable for formation of a small diameter via hole.
However, the excimer laser results in rise of product cost, when it is introduced into the industrial use, because the apparatus cost becomes high, and further, parts such as lens are easily deteriorated because of short wavelength and these parts must be replaced frequently, and the expensive excimer gas must be supplemented and replaced within a short period.
Regarding this point, the CO2 laser having a relatively longer wavelength is rather suitable for industrial use because not only output level is high and the apparatus cost is low but also repair of lens, for example, is not required and supplement of CO2 laser can be realized at a low price, however when laser beam output is raised to form a deeper hole, hole diameter of via hole becomes larger. In addition, the hole in diameter of 100 μm which is about 10 times the wavelength (10.6 μm) can be bored easily but the hole in diameter of 50 μm or less which is about 5 times the wavelength is bored with considerable difficulty.
Such problem is generated also when the CO2 laser is used as the laser source for processing, in addition to the multilayer printed wiring board.
Moreover, in the manufacturing apparatus of a multilayer printed wiring board of the related art, since several thousands to several tens of thousand via holes are bored in the multilayer printed wiring board, a longer time has been required to bore the holes of only one layer with the laser and the processing time becomes very long when such laser process is repeated for multiple layers.